Industrial plants having containers or tanks (“tanks”) generally need to regularly measure the level of liquid(s) or other materials therein such as powders. There are several types of systems and techniques used for level measurement, which generally utilize time domain reflectometry (TDR) which relies on analyzing echoes.
For TDR-based measurements, there are contact level measurements, where a part of the system, such as a probe, contacts the material being measured, and non-contact level measurements where the level is measured with a probe without contacting the material to be measured. Non-contact methods include ultrasound which uses high-frequency sonic (sound) waves to detect the level, and radar which uses electromagnetic energy at radio frequencies which propagate through free space.
Guided wave radar (GWR) is a particular contact pulsed radar method used to measure the level of liquids or solids in a tank. GWR works by generating a stream of pulses of electromagnetic energy and propagating the pulses down a transmission line formed into a level sensing probe. The probe is generally placed vertically in a tank or other container and the electromagnetic pulse is launched downward from the top of the probe. The probe is open to both the air and the material(s) to be sensed in such a way that the electromagnetic fields of the propagating pulse penetrate the air (or other gas, liquid or perhaps a solid) until they reach the level of the product material. At that point, the electromagnetic fields see the higher dielectric constant of the product material. This higher dielectric constant causes a reduction in the impedance of the transmission line, resulting in a pulse echo being reflected back to the top of the probe. The pulse travels through the generally air dielectric portion of the probe above the product material at a known velocity. Knowing both the return trip time of the radar pulse and the dielectric constant of the material through which the radar pulse propagates allows the material level(s) on the probe to be determined.
When installing a pulsed radar level gauge on a tank for the first time or when troubleshooting an existing pulsed radar level gauge installation, software-based set-up tools are typically used as a setup aid. These set-up tools are used to program the pulsed radar level gauge with such parameters as waveguide length, tank nozzle dimensions (for tanks having nozzles), product material(s) in the tank (their dielectric constants), and expected tank disturbances (e.g., foam, turbulence). In addition to setting up the pulsed radar level gauge and application parameters, the set-up tool is generally also used to collect and display actual echo curves received responsive to transmitted radar pulses. Such displayed actual echo curves are then used by the operator (e.g., technician or engineer) to judge whether the pulsed radar level gauge has been set-up and is operating as expected, and this judgment is dependent upon the experience and expertise of the pulsed radar level gauge operator.